The additional security measures were put in place following intelligence reports, said an official at the civil aviation ministry, who spoke on condition of anonymity because of the issue is sensitive.

The official didn't elaborate, but the CNN-IBN television station reported that a U.S. Internet center received an e-mail saying there were plans to hijack a U.S. or Europe-bound flight from India. The center handed the e-mail to the FBI which informed Indian intelligence, the report said.

The report did not say who sent the e-mail or if any particular airport or airline was at risk. It did not explain what an Internet center is.

Only days earlier, a letter warning of imminent attacks at airports or on aircraft in southern India prompted officials to issue a security alert for airports there. The letter was sent to the director of the domestic airport in the southern city of Trichy.

Authorities said they were investigating the letter, which was written in Tamil. Its sender described himself as an Al Qaeda supporter.

On Sunday, police erected barricades on roads leading to airports in major cities including New Delhi, Mumbai, Bangalore and Chennai.

Kumar at the Chennai airport said that the extra security measures will not lead to delays.

"There is no need to panic. There is no need (for passengers) to come early," he said.